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...cell embryo doesn't count as a human life in the first place--not when compared with the life it could help save. Opponents say the promise of embryo research has been oversold, and they point to the cures that have been derived from adult stem cells from bone marrow and umbilical cords; supporters retort that adult stem cells are still of limited use, and to fully realize their potential we would need to know more about how they operate--which we can learn only from studying leftover fertility-clinic embryos that would otherwise be thrown away...
...than scientists initially hoped. Although about 90% of cord-blood stem cells are precursors for blood and immune cells, the remaining 10% give rise to liver, heart-muscle and brain cells and more. Over the past five years, cord-blood transplants have become an increasingly popular alternative to bone-marrow transplants for blood disorders, particularly when a bone-marrow match can't be found...
Less plastic than cord-blood cells are adult stem cells, which until recently researchers thought couldn't do much more than regenerate cell types that reflected the stem cells' origin--blood and immune cells from bone marrow, for example. Even so, some scientists believe adult stem cells may prove to be a powerful source of therapies. "In some cases, you may not want to go all the way back to embryonic stem cells," says Kurtzberg. "You may want something more specific or less likely to stray. You wouldn't want to put a cell in the brain and find...
...good news for all sides is that over the course of this long argument, researchers have learned more about how stem cells work, and the science has outrun the politics. Adult cells, such as those found in bone marrow, were thought to be less valuable than embryonic cells, which are "pluripotent" master cells that can turn into anything from a brain cell to a toenail. But adult cells may be more elastic than scientists thought, and could offer shortcuts to treatment that embryonic cells can't match...
Researchers have discovered that many tissues and organs contain precursor cells that act in many ways like stem cells. The skin, intestines, liver, brain and bone marrow contain these stem cell-- mimicking cells, which could become a reservoir of replacement cells for treating diseases such as leukemias, stroke and some cancers. "Brain stem-cells can make almost all cell types in the brain, and that may be all we need if we want to treat Parkinson's disease or ALS," says Dr. Arnold Kriegstein, who directs the University of California at San Francisco's Institute for Regeneration Medicine. "Embryonic stem...